1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Background
Electrophotographic image forming apparatuses transfer a toner image formed on an image carrier onto a recording sheet at a transfer unit, and then heat and press the recording sheet at a fixing unit so as to fix the toner image on the recording sheet, thus forming an image. At the time when the recording sheet is separated from the image carrier after the toner image has been transferred onto the recording sheet from the image carrier, shearing force is generated between the toner transferred to the recording sheet side and the toner remaining on the image carrier. As a result, the toner can scatter from the shear plane. Even though some of the toner remain on the image carrier, the level of charging of the remaining toner is low, which causes the remaining toner to scatter due to the rotation force of the image carrier. Thus, the toner scatters and flows in the conveyance path, and in addition to the toner, powder dust also flows in the conveyance path. The powder dust results from recording sheet fiber and additive resulting from friction between the transfer roller and the recording sheet.
In an attempt to reduce such powder dust, Japanese Unexamined Patent Application Publication No. 2011-123387 discloses an image forming apparatus that arranges a suction port of a suction device, which sucks powder dust such as flowing toner, adjacent to a second transfer cleaning device, which removes toner remaining on a second transfer belt. The image forming apparatus recited in Japanese Unexamined Patent Application Publication No. 2011-123387 passes a recording sheet through an intermediate transfer belt and the second transfer belt so as to transfer a toner image on the intermediate transfer belt onto the recording sheet. In this configuration, the suction port of the suction device is disposed adjacent to the second transfer belt on the back surface of the recording sheet (which is the side on which no image is formed). This ensures that powder dust sucked through the suction port is collected by a filter in the suction device.
The powder dust resulting from flowing toner and recording sheet fiber flowing in the conveyance path attaches to and accumulates on a conveyance guide and other elements that constitute the conveyance path. Thus, when the recording sheet conveyed through the conveyance path comes to the conveyance guide, the recording sheet contacts the conveyance guide due to the charging state of the recording sheet or similar causes, powder dust and other substances attach on the recording sheet. This results in noise generated in the image on the recording sheet. In this respect, even though the image forming apparatus recited in Japanese Unexamined Patent Application Publication No. 2011-123387 provides a suction device, the suction device performs its suction on the opposite side of the image formation surface of the recording sheet, instead of removing powder dust on the side of the image formation surface. Thus, the image forming apparatus recited in Japanese Unexamined Patent Application Publication No. 2011-123387 can be insufficient for reducing image noise.
In the conveyance path between the transfer unit and the fixing unit, the passage of the recording sheet and the rotation of the intermediate transfer belt cause the air in the conveyance path to flow in the recording sheet movement direction and in the belt rotation direction. Additionally, closed space is defined by the recording sheet and the intermediate transfer belt, and this makes the upstream side in the recording sheet conveyance direction into negative pressure. This causes another flow of air, in addition to the above-described flow of air, in a direction opposite the recording sheet conveyance direction along the guide member on the downstream side of the intermediate transfer belt. That is, in the conveyance path, flows of air occur in the recording sheet conveyance direction and in the opposite direction. These flows of air cause a swirling current, which in turn causes the toner to be swirled up to attach to the recording sheet, resulting in occurrence of image noise.
The present invention has been made in view of the above-described circumstances, and it is an object of the present invention to provide an image forming apparatus capable of preventing flowing toner and other substances in the conveyance path for the recording sheet from attaching to the recording sheet loaded with a transferred toner image, thereby minimizing occurrence of image noise.